System and method for detecting cyanide exposure

ABSTRACT

In an example, a method of detecting cyanide exposure of an individual comprises measuring a thiocyanate level of the individual, and comparing the measured thiocyanate level to a preset thiocyanate threshold to determine whether the measured thiocyanate level is above the preset thiocyanate threshold indicating a level of acute cyanide poisoning for which medical treatment is recommended to treat health effects of the exposure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a nonprovisional of and claims the benefit ofpriority from U.S. Provisional patent application No. 63/036,225, filedon Jun. 8, 2020, entitled SYSTEM AND METHOD FOR DETECTING CYANIDEEXPOSURE, the disclosure of which is incorporated by reference in itsentirety.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support, provided by the UnitedStates Department of Homeland Security, via DTIC contractFA8075-14-D-0003, and by an employee of the United States Department ofHomeland Security in the performance of their official duties. The U.S.Government has certain rights in this invention.

FIELD

The discussion below relates generally to systems and methods ofdetecting chemical exposure and, more particularly, to the detection ofcyanide exposure.

BACKGROUND

On average, each year more than 3,000 Americans die and more than 14,000are injured as a result of injuries sustained from fires in the UnitedStates. In 2017, for instance, there were 1,319,500 fires in the UnitedStates, approximately 30% of which were residential and non-residentialbuilding fires. There were 14,670 injuries and 3,400 deaths with most ofboth categories resulting from smoke inhalation. In addition, 4,510firefighters were reported as being injured by smoke inhalation, 550suffered heart attacks, and 850 had other respiratory distress. Of the550 heart attacks, 50 fatalities were reported. Only recently has themedical community understood the consequences of cyanide poisoningassociated with building fires and the need to address this potentialthreat. The most common cause of death in fires is the inhalation ofnoxious gases rather than thermal injury. Hydrogen cyanide gas, the mosttoxic product of combustion, seldom was recognized as a significanthazard in smoke inhalation. Even the most heroic efforts wereineffective if life-saving oxygen is blocked from the cells by cyanide.

Although cyanide is suspected of playing a role in smoke inhalationinjury and death, definitive correlations of the role of cyanide havenot been made because of the complex nature of fire smoke toxins andexposure. Nonetheless, that cyanide exposure has been a factor infatalities is established. Cyanide intoxication can lead to death byceasing cellular respiration or contributing to a heart attack.

One of the challenges with cyanide poisoning is that it is hard tomeasure in an exposed individual. Timely administration of the antidoteis important to treat the exposed individual, but the high cost oftreatment renders it difficult to justify its use without more reliableproof that the individual is indeed suffering from cyanide poisoning.

SUMMARY

Embodiments of the present invention are directed to a fast, on-scenetest for presumptively identifying if a smoke exposed person has inhaleda dangerous amount of cyanide gas. Carbon monoxide (CO) and hydrogencyanide (HCN) are the toxic twins of smoke inhalation. In one example,detection of intoxication by CO can be performed quickly and easilyon-site with a modern pulse oximeter.

Heretofore, there has been no widely available, affordable, rapid,confirmatory cyanide exposure test such as a cyanide blood test.Assessment of cyanide exposure levels is difficult. Detection of cyanideexposure is not performed by instrument. Firefighters and medicalpersonnel are trained to watch for signs and symptoms of cyanideexposure, but this can be problematic since many cyanide/HCN physicalindicators are similar to, or disguised by, CO signs and symptoms.Cyanide intoxication can be treated. Responders have to rely on gettingthe exposed individual to the hospital for treatment where treatmentdecisions are made on the basis of clinical history and signs andsymptoms of cyanide intoxication.

While detection of cyanide in blood is difficult, it is possible todetect thiocyanate in saliva. Thiocyanate is formed as a direct responseof the body to detoxify cyanide, which is a naturally occurringsubstance and relatively harmless in normal dietary amounts. Inaddition, the presence of methemoglobin, which captures and temporarilyholds some of the cyanide, in an individual may suggest that little orno free cyanide is available for binding. A substantial reduction of themethemoglobin in a cyanide exposed individual may indicate that thecapacity for conversion to thiosulfate has been exceeded. While asignificantly elevated salivary thiocyanate above a threshold level isbelieved to be a sufficient basis to indicate that the main cyanidedetoxification mechanisms have been overwhelmed in a cyanide exposedindividual, a combination of elevated salivary thiocyanate and depressedmethemoglobin values may provide an even stronger basis by taking intoaccount variations in endogenous cyanide levels in differentindividuals. Measuring these two parameters could provide a morereliable screening method for cyanide intoxication.

In one embodiment a screening method for cyanide intoxication is basedon measuring the presence or absence of elevated salivary thiocyanateand depressed methemoglobin values. First, a screening test for highthiocyanate levels is possible based on the reaction with iron nitrate.For instance, the exposed individual can have a saliva sample taken andcontacted with a sample collection device (e.g., a swab or a strip) witha colorimetric indicator such as iron nitrate to indicate highthiocyanate levels in saliva. Second, pulse oximetry can measure lowmethemoglobin to indicate that methemoglobin is no longer available tobind with cyanide. A substantial reduction of methemoglobin in a cyanideexposed individual indicates that the capacity for conversion tothiosulfate has been exceeded. It is believed that high salivarythiocyanate levels will presumptively indicate that a toxic exposure tocyanide has occurred. Methemoglobin levels may add further confirmationor refinement to determining a level of salivary thiocyanate thatindicates further medical treatment or screening is needed. Pulseoximetry can also measure carboxyhemoglobin to assess the exposure to COwhich could adjust the danger level of cyanide exposure. In anotherembodiment, the first measurement alone may be adequate to indicate thatthe natural detoxification methods in the body are overwhelmed.

In one example, a saliva sample from a potentially exposed person can beplaced in contact with a simple chemical indicator that will indicate,in conjunction with pulse oximetry measurements, whether or not ahigh-level cyanide exposure has occurred. Now victims of building firesand hazardous materials incidents can experience the benefits of anantidote sooner. This invention will likely save lives, since the singlemost important factor driving successful conversion of a potentiallylethal exposure of cyanide into full recovery is timeliness of rescue.

In accordance with an aspect of the present disclosure, a method ofdetecting cyanide exposure of an individual comprises measuring athiocyanate level of the individual, and comparing the measuredthiocyanate level to a preset thiocyanate threshold to determine whetherthe measured thiocyanate level is above the preset thiocyanate thresholdindicating a level of acute cyanide poisoning for which medicaltreatment is recommended to treat health effects of the exposure.

In accordance with another aspect of the disclosure, a method ofdetecting cyanide exposure of an individual, the method comprising:measuring a thiocyanate level of the individual; comparing the measuredthiocyanate level to a first preset thiocyanate threshold to determinewhether the measured thiocyanate level is above the first presetthiocyanate threshold; if the measured thiocyanate level is above thefirst preset thiocyanate threshold, recommending further medicalassessment possibly leading to treatment to treat health effects of theexposure; if the measured thiocyanate level is not above the firstpreset thiocyanate threshold, then performing at least one of thefollowing two processes. The first process includes measuring amethemoglobin level of the individual, comparing the measuredthiocyanate level to a second preset thiocyanate threshold, which islower than the first preset thiocyanate threshold, to determine whetherthe measured thiocyanate level is above the first preset thiocyanatethreshold, comparing the measured methemoglobin level to a presetmethemoglobin threshold to determine whether the measured methemoglobinlevel is below the preset methemoglobin threshold, and if the measuredthiocyanate level is above the first preset thiocyanate threshold andthe measured methemoglobin level is below the preset methemoglobinthreshold, recommending medical treatment to treat health effects of theexposure. The second process includes measuring a carboxyhemoglobinlevel of the individual, comparing the measured thiocyanate level to athird preset thiocyanate threshold, which is lower than the first presetthiocyanate threshold, to determine whether the measured thiocyanatelevel is above the first preset thiocyanate threshold, comparing themeasured carboxyhemoglobin level with a preset carboxyhemoglobinthreshold to determine whether the measured carboxyhemoglobin level isabove the preset carboxyhemoglobin threshold, and if the measuredthiocyanate level is above the first preset thiocyanate threshold andthe measured carboxyhemoglobin level is above the presetcarboxyhemoglobin threshold, recommending medical treatment to treathealth effects of the exposure.

In accordance with another aspect of this disclosure, a method ofdetecting cyanide exposure of an individual comprises: determining apreset thiocyanate threshold; measuring a thiocyanate level of theindividual; and comparing the measured thiocyanate level to the presetthiocyanate threshold to determine whether the measured thiocyanatelevel is above the preset thiocyanate threshold indicating a level ofacute cyanide poisoning for which medical treatment is recommended totreat health effects of the exposure. Determining the preset thiocyanatethreshold includes: measuring thiocyanate levels of a plurality ofunexposed individuals who have not been exposed to cyanide; measuringthiocyanate levels of a plurality of exposed individuals after anexposure of the plurality of exposed individuals to cyanide; monitoringthe plurality of exposed individuals after the exposure for healtheffects of the exposure; identifying, out of the plurality of exposedindividuals being monitored, one or more harmed individuals for whommedical treatment is recommended to treat the health effects of theexposure; comparing the thiocyanate levels of the plurality of unexposedindividuals, the thiocyanate levels of the one or more harmedindividuals, and the thiocyanate levels of the plurality of exposedindividuals after the exposure who are not the one or more harmedindividuals; determining, based on the comparing, a thresholdthiocyanate level above which medical treatment is recommended to treatthe health effects of the exposure; and setting the thresholdthiocyanate level as the preset thiocyanate threshold.

Other features and aspects of various examples and embodiments willbecome apparent to those of ordinary skill in the art from the followingdetailed description which discloses, in conjunction with theaccompanying drawings, examples that explain features in accordance withembodiments. This summary is not intended to identify key or essentialfeatures, nor is it intended to limit the scope of the invention, whichis defined solely by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The attached drawings help explain the embodiments described below.

FIG. 1 shows the cyanide metabolism after it enters the bloodstream.

FIG. 2 includes two tables. Table 1 shows preparation of standardsolutions for determination of the molar absorption coefficient ofFeSCN²⁺ complex. Table 2 shows measurement of saliva thiocyanateconcentration.

FIG. 3 includes Table 3 which shows average cyanide and thiocyanatelevels (μM) in blood and salivary samples taken from healthy volunteers.

FIG. 4 includes Table 4 which shows thiocyanate levels in plasma andsaliva of nonsmokers and smokers (MV±SD).

FIG. 5 shows a scatter diagram of carboxyhemoglobin (COHb) versusthiocyanate (SCN) values in 439 adults with the line of discriminationbetween smokers and non-smokers.

FIG. 6 shows serum thiocyanate levels in nonexposed control subjectscompared to exposed firefighters (all smoking categories).

FIG. 7 includes Table 5 which lists reported endogenous concentrationsof cyanide in various biological samples from human smokers andnon-smokers.

FIG. 8 illustrates the relationships of cyanide concentrations in bloodof fire victims and controls.

FIG. 9 shows an example of a flow diagram illustrating a method ofdetecting cyanide exposure.

FIG. 10 shows an example of a flow diagram illustrating another methodof detecting cyanide exposure.

FIG. 11 shows an example of a salivary thiocyanate levels generated forfour groups: Healthy, Periodontitis, Smokers, and Gutka chewers.

FIG. 12 shows the degree of color change with different concentrationsof thiocyanate according to one example.

FIG. 13 shows notional different categories of concern based on thedegree of color change with different concentrations of thiocyanate.

DETAILED DESCRIPTION

A number of examples or embodiments of the present invention aredescribed, and it should be appreciated that the present inventionprovides many applicable inventive concepts that can be embodied in avariety of ways. The embodiments discussed herein are merelyillustrative of ways to make and use the invention and are not intendedto limit the scope of the invention. Rather, as will be appreciated byone of skill in the art, the teachings and disclosures herein can becombined or rearranged with other portions of this disclosure along withthe knowledge of one of ordinary skill in the art.

In firefighting, CO is generally the more prevalent substance found inresidential fires, but cyanide is much more toxic. Both CO and cyanideinhibit the use of oxygen by cells: CO by blocking adsorption of oxygenby hemoglobin and cyanide by blocking cellular respiration. The effectsof these two gasses are thought to be additive and fatalities haveoccurred with less than fatal levels of each substance alone. Rapidon-site detection of health threatening exposure is limited to CO, viathe formation of carboxyhemoglobin, pulse oximetry. Detection of HCNexposure cannot be easily, or quickly, performed and is recommended tobe done by observation of potential victim's signs and symptoms.

Cyanide is suspected of playing a role in heart attacks. It is known tocause heart arrhythmias but direct connection to cyanide exposure hasnot been firmly correlated to a fire smoke environment. Furthermore,other heart stressors such as CO and particulate exist in a fire smokeenvironment.

Cyanides are well absorbed via the gastrointestinal tract or skin andrapidly absorbed via the respiratory tract. Once absorbed, cyanide israpidly and ubiquitously distributed throughout the body, although thehighest levels are typically found in the liver, lungs, blood, andbrain. There is no accumulation of cyanide in the blood or tissuesfollowing chronic or repeated exposure.

Approximately 80% of absorbed cyanide is initially metabolized tothiocyanate in the liver by the mitochondrial sulfur transferase enzymerhodanese and other sulfur transferases. Thiocyanate is excreted in theurine. Minor pathways for cyanide detoxification involve reaction withcystine to produce aminothiazoline-carboxylic andiminothiazolidinecarboxylic acids and combination with hydroxycobalamin(vitamin B_(12a)) to form cyanocobalamin (vitamin B₁₂); theseend-products are also excreted in the urine. See FIG. 1.

Cyanide is naturally occurring and mechanisms to cope with cyanideexposure already exist within the body. The major route is formation ofthiocyanate until the sulfur donors are depleted. Thiocyanate (SCN⁻) isrelatively non-toxic and concentrates in the saliva. It is more stablein the blood stream but variable between person to person. Studies havedemonstrated that smokers can be distinguished from non-smokers bysalivary SCN⁻. Only when the detoxification mechanisms are overwhelmeddoes serious injury from cyanide begin. Cyanide and cyanidedetoxification chemicals show up in red blood cells, blood plasma,saliva, and urine. These mechanisms can provide the information thattells what level of cyanide is in the body.

FIG. 1 shows the cyanide metabolism after it enters the bloodstream.ATSDR, Toxicological Profile for Cyanide (July 2006). The majordetoxification route for cyanide is conversion to the less toxicthiocyanate (SCN⁻) catalyzed by the enzyme rhodanese. Animal studiesindicate that this is the major metabolic pathway for cyanidedetoxification with about 80% of the initial cyanide exposure convertedto thiocyanate:HCN/CN⁻+Sulfur Donor←Rhodanese→SCN

This causes a spike in blood thiocyanate levels. Conversion, however, islimited by the amount of sulfur donors, mainly thiosulfate, available.One medical treatment method for cyanide exposed individuals includesadministration of sodium thiosulfate to boost sulfur donors. A secondmechanism for cyanide detoxification occurs when cyanide in the redblood cells binds with methemoglobin, to form cyanomethemoglobin, whichis relatively non-toxic and holds the cyanide for eventual eliminationthrough the thiocyanate pathway. Methemoglobin is normally between 0.25%and 1% of hemoglobin and, at normal levels, can bind approximately 10 mgof cyanide. Another medical treatment method for cyanide exposure isadministration of amyl nitrate, or similar compound, which increasesblood methemoglobin. Through the detoxification mechanisms, the rate ofdetoxification of HCN in humans may be about 0.017 mg CN/kg*min asreported by McAllister citing Ballantyne in McAllister et al., Stabilityof CN in cadavers J. Anal. Tox. 2008, or about 1 mg CN/kg/Hr as reportedby Ketha and Garg in Hema Ketha, Uttam Garg. Toxicology Cases for theClinical and Forensic Laboratory, Academic Press 2020, accessed Apr. 1,2021,http://search.ebscohost.com/login.aspx?direct=true&db=nlebk&AN=2226023&site=eds-live.

Pulse oximetry, the measurement of transmission of specific lightfrequencies across the finger or earlobe, has advanced to point wheredetection of oxyhemoglobin, reduced hemoglobin (deoxygenatedhemoglobin), methemoglobin, and carboxyhemoglobin are routinelyperformed. Carboxyhemoglobin is especially critical as it is the toxicactor for CO poisoning. In the future, it may be possible to use pulseoximetry, or related technology, to measure cyanomethemoglobin; however,it is likely that difficulties in concentration, pulse oximeters measureconstituents as a percentage where cyanide components exist at the micromolar range, and interference from other substances, have prevented thisfrom reaching the marketplace to date. As a result, cyanide intoxicationis usually diagnosed clinically based on signs and symptoms becauseclinical test results may not be available for hours or days.

Measurement of the methemoglobin level is especially important incyanotic patients. The presence of methemoglobin suggests that little orno free cyanide is available for binding because methemoglobinvigorously binds cyanide to form cyanomethemoglobin (which is notmeasured by pulse oximetry as methemoglobin). A substantial reduction ofthe methemoglobin in a cyanide exposed individual could indicate thatthe capacity for conversion to thiosulfate has been exceeded.

The levels of cyanide and thiocyanate have been reported for smokers,non-smokers, firefighters, and victims. The reporting reveals thatsalivary thiocyanate levels show a very large range between subjects,but the levels in saliva are much higher than cyanide or thiocyanatelevels in other biological fluids. FIG. 2 includes two tables. Table 1shows preparation of standard solutions for determination of the molarabsorption coefficient ε of FeSCN²⁺ complex. Six solutions in test tubeswere prepared for the determination of ε of FeSCN²⁺ complex according toTable 1. Table 2 shows measurement of saliva thiocyanate concentration.The qualitative and quantitative analysis of thiocyanate ion in humansaliva was performed as a part of the exercise to determine the chemicalequilibrium between Fe³⁺ and SCN⁻ ions. The results are collected inTable 2. The saliva thiocyanate ion concentration of 147 subjects variedfrom 0.4 to 5.6 mM. It is clearly demonstrated that cigarette smokers(ca. 10%) tend to have higher SCN⁻ concentration than the nonsmokers.Tables 1 and 2 are disclosed in Lahti et. al., SpectrophotometricDetermination of Thiocyanate in Human Saliva, J. Chemical Education,Vol. 76, No. 9, 1281-82 (1999).

FIG. 3 includes Table 3 which shows average cyanide and thiocyanatelevels (μM) in blood and salivary samples taken from healthy volunteers.The salivary cyanide levels in the smokers are significantly higher thanthose in the nonsmokers. Table 3 is disclosed in Tsuge et al., Cyanideand Thiocyanate Levels in Blood and Saliva of Healthy Adult Volunteers,J. Health Science 46(5) 343-350 (2000). FIG. 4 includes Table 4 whichshows thiocyanate levels in plasma and saliva of nonsmokers and smokers(MV±SD). Compared with non-smokers, smokers show 2 to 3 times higherthiocyanate levels. Table 4 is disclosed in Biomonitoring MethodsThiocyanate in Plasma and Saliva, MAK Collection, Vol. 13 (2013).

Carboxyhemoglobin and plasma thiocyanate concentrations were measured in79 non-smokers and 360 cigarette smokers in the study by Soloojee et.al., Carboxyhemoglobin and plasma thiocyanate complementary indicatorsof smoking behavior, Thorax 37, 521-525 (1982). FIG. 5 is disclosed inSoloojee et al. and shows a scatter diagram of carboxyhemoglobin (COHb)versus thiocyanate (SCN) values in 439 adults with the line ofdiscrimination between smokers and non-smokers. The dashed lines are thelimiting values of 1-6% COHb and 73 μmol SCN/l. Based on FIG. 5, itappears that plasma offers the best differentiation between thiocyanateconcentrations found in smokers and non-smokers.

The relationship of thiocyanate with fire smoke exposure can be inferredfrom a 1973/74 study of Baltimore firefighters. Serum thiocyanate wasmeasured from blood samples drawn from firefighters on-site immediatelyafter the firefighter left the fire atmosphere. Maximum serumthiocyanate was highest for the firefighters regardless of smokingcategories; however, some exposed firefighters had lower levels thancontrol subjects. FIG. 6 shows serum thiocyanate levels in nonexposedcontrol subjects compared to exposed firefighters (all smokingcategories). FIG. 6 is disclosed in Levin and Radford, OccupationalExposures to Cyanide in Baltimore Fire Fighters, J. OccupationalMedicine, Vol. 20, No. 1 (January 1978). For that study, no firefighterwas reported as suffering from cyanide intoxication indicating that thelevels reported, though high, might not be as high as a presumptivescreening test would need to be.

Comparing FIG. 4 to FIG. 6, one can see that the thiocyanate (SCN⁻) inplasma shown in FIG. 4 compares well to the controls in FIG. 6 (aug/ml=mg/l). FIG. 4 shows corresponding salivary thiocyanate levels 15to 20 times higher, which makes detection easier.

Thiocyanate (rhodanide) is the main metabolite of cyanide and can thusbe used as biomarker for exposure to cyanide or to cyanide releasingchemicals. Especially for chronic exposure to low cyanide concentrations(e.g., exposure from smoking or at certain workplaces), thiocyanate inplasma and saliva is a suitable biomarker. An aspect of the detectionmethodology is based on the rapid and reliable determination ofthiocyanate in saliva using a photometric method. When Fe(III) ions areadded to samples containing thiocyanate, a red complex is formed, whichis measured close to its absorption maximum at 492 nm.

The photometric method permits the quantitative determination ofthiocyanate in small sample volumes and with a short sample preparationtime. One approach uses a plate reader by adaption to microtiter platesand is particularly suitable for the determination of large samplenumbers. The thiocyanate levels in saliva are approximately 20 timeshigher than the corresponding levels in plasma (see Table 4 in FIG. 4).This is probably due to active secretion of the thiocyanate ion via thesalivary glands. Furthermore, thiocyanate concentrations in salivastrongly depend on salivary flow. For this reason, thiocyanate levels insaliva are, despite better precision, subjected to greaterintra-individual variations than thiocyanate levels in plasma. Owing tothe long half-life of thiocyanates, i.e., 6-14 days, this biomarkerought to be especially suitable for determining chronic exposures to lowcyanide concentrations. For the given reasons, this at least applies tothiocyanate in saliva to a limited extent.

Various cyanide detection scheme candidates are considered. In terms ofarterial and venous blood gases, cyanide toxicity is characterized by anormal arterial oxygen tension and an abnormally high venous oxygentension, resulting in a decreased arteriovenous oxygen difference(<10%). A high-anion-gap metabolic acidosis is a hallmark of significantcyanide toxicity. Apnea may result in combined metabolic and respiratoryacidosis. In terms of blood lactate level, elevation in the bloodlactate level is a sensitive marker for cyanide toxicity. A plasmalactate concentration of greater than 10 mmol/L in smoke inhalation orgreater than 6 mmol/L after reported or strongly suspected pure cyanidepoisoning suggests significant cyanide exposure. With regard to redblood cell or plasma cyanide concentration, cyanide blood concentrationsare not generally available in time to aid in the treatment of acutepoisoning but may provide subsequent confirmation. In cyanogenexposures, these tests provide documentation for therapeutic use, whichmay last several days. The preferred test is a red blood cell cyanideconcentration. With this method, mild toxicity is observed atconcentrations of 0.5-1.0 μg/mL. Concentrations of 2.5 μg/mL and higherare associated with coma, seizures, and death. Blood cyanideconcentrations may artificially increase after sodium nitrite (antidote)administration, because of in vitro release of cyanide fromcyanomethemoglobin during the analytical procedure by strong acid usedin analysis.

Because CO and HCN are the toxic twins of smoke inhalation, detection ofCO poisoning is part of the present methodology. One approach is basedon measuring carboxyhemoglobin level to determine blood carbon monoxideconcentration. Carboxyhemoglobin (HbCO) level (by co-oximetry) or bloodcarbon monoxide concentration (by infrared spectroscopy) may be obtainedin patients with smoke inhalation to rule out concurrent exposure. HbCOmeasurements may be artificially elevated in blood samples drawn afterhydroxocobalamin administration.

The chosen candidate involves the detection of a methemoglobin level,which is especially important in cyanotic patients. The presence ofmethemoglobin suggests that little or no free cyanide is available forbinding because methemoglobin vigorously binds cyanide to formcyanomethemoglobin (which is not measured as methemoglobin by pulseoximetry). Methemoglobin concentrations provide a guide for continuedtherapy after the use of methemoglobin inducing antidotes, such assodium nitrite. Elevated levels of methemoglobin (>10%) indicate thatfurther nitrite therapy is not indicated and, in fact, may be dangerous.

When analyzing for cyanide exposure, it is important to note that allbiological samples will contain endogenous levels of cyanide (and itsbiological markers). Therefore, baseline levels of the analyte (cyanide,thiocyanate, ATCA, or cyanide-protein adducts) should be known prior toconcluding the occurrence of a cyanide exposure. FIG. 7 includes Table 5which lists reported endogenous concentrations of cyanide in variousbiological samples from human smokers and non-smokers. Table 5 isdisclosed in Textbook of Military Medicine, Chapter 11, 371-410.

A study in Paris withdrew blood from 109 victims of fire by the firstmedical team to reach the scene. Blood cyanide was measured and levelsshowed measurable differences between control subjects, victims whosurvived, and victims who died. FIG. 8 illustrates the mean (±SD) bloodcyanide concentrations in the control subjects, the fire victims whodied, and the victims who survived. Of the 109 fire victims from whomblood specimens were obtained, 43 died (39 percent). The mean bloodcyanide concentration in these 109 patients was 59.0±77.9 μmol perliter. In those who died, it was 116.4±89.6 μmol per liter, and in thosewho survived it was 21.6±36.4 μmol per liter. All these values weresignificantly higher than those for the control group. The correspondingmean blood carbon monoxide concentration in the 109 fire victims was1.5±1.7 mmol per liter. In those who died it was 2.8±2.0 mmol per liter,and in those who survived it was 0.7±0.7 mmol per liter. FIG. 8 isdisclosed in Baud et. al., Elevated Blood Cyanide Concentrations inVictims of Smoke Inhalation, New England J. Medicine 325, 1761-1766(1991).

The analytical determination of biological markers of cyanide exposureis not an easy task due to chemical properties, biological activities,and limited published research (for certain markers of cyanideexposure). Different approaches have their own advantages anddisadvantages. For thiocyanate, the main drawback is large and variablebackground concentrations in biological samples. Other disadvantagesinclude the conversion of cyanide and thiocyanate and the use ofthiocyanate by other biological processes not directly related tocyanide metabolism.

Cyanide Exposure Detection Methodology

FIG. 9 shows an example of a flow diagram 900 illustrating a method ofdetecting cyanide exposure. The method is based on measuring thepresence or absence of elevated salivary thiocyanate and can be combinedwith measuring depressed methemoglobin values and/or with measuringelevated carboxyhemoglobin values. A fast, on-site, lifesaving test forcyanide intoxication in firefighters and smoke victims is presented.

First, the thiocyanate level is measured (step 910) to test for a highthiocyanate level above a preset thiocyanate threshold, whichdistinguishes between salivary thiocyanate levels of concern and levelsnot of concern. The comparison (912) and determination of an elevatedthiocyanate level above the preset thiocyanate threshold (determination914) leads to a conclusion of a dangerous level of acute cyanidepoisoning (conclusion 916). That is, the result of the comparisonindicates a level of acute cyanide poisoning for which medical treatmentis recommended (and may be needed or required) to treat the healtheffects of the exposure. For instance, the exposed individual can use asimple chemical indicator (e.g., a swab or strip with a colorimetricindicator such as iron nitrate) to indicate the presence of a highthiocyanate level in saliva.

The thiocyanate measurement step 910 finds support in Table 2 in FIG. 2,which shows the results reported for students as a chemistry laboratoryexperiment based on using Fe(NO₃)₃ and reacting it with SCN⁻:Fe³⁺(aq)+SCN⁻(aq)↔FeSCN²⁺(aq)

The thiocyanoiron (II) ion is a deep red color that absorbs at 477 nm. Alow-cost sample collection device (e.g., a swab or a strip) with acolorimetric indicator such as iron nitrate can be used to test for thepresence of a high thiocyanate level in saliva.

Second, the methemoglobin level is measured to test for a lowmethemoglobin level below a preset methemoglobin threshold (step 920).The comparison (922) and determination of a depressed methemoglobinlevel below the preset methemoglobin threshold (determination 924), whencombined with an elevated thiocyanate level above the preset thiocyanatethreshold (determination 914), leads to a conclusion of a more clearlydangerous level of acute cyanide poisoning (conclusion 926). That is, adetermination that the measured thiocyanate level is above the presetthiocyanate threshold and the measured methemoglobin level is below thepreset methemoglobin threshold provides a more reliable or clearer orfurther indication of acute cyanide poisoning for which medicaltreatment is recommended to treat the health effects of the exposure.For instance, pulse oximetry can measure low methemoglobin to indicatethat methemoglobin is no longer available to bind with cyanide in theexposed individual. A substantial reduction of methemoglobin in acyanide exposed individual indicates that the capacity for conversion tothiosulfate has been exceeded. In one example, pulse oximetry involvesthe measurement of transmission of specific light frequencies across thefinger or earlobe.

The first comparison determination of elevated salivary thiocyanatedetection (determination 914) may be sufficient, and the secondcomparison determination of depressed methemoglobin detection(determination 924) may not be necessary. As discussed above, whenanalyzing for cyanide exposure, because all biological samples willcontain endogenous levels of cyanide, some way of accounting for that isdesirable in determining whether a sample contains a dangerous level ofcyanide. The second comparison determination of depressed methemoglobindetection (determination 924) is used to take into account variations ofendogenous levels of cyanide in different individuals so as to minimizeor avoid false positives. Combined, these two measurements provide amore reliable basis or a further basis to indicate that the naturaldetoxification methods in the body are overwhelmed.

Third, the carboxyhemoglobin level is measured to test for exposure toCO (step 930). For instance, pulse oximetry can also be used to measurecarboxyhemoglobin to assess the exposure to CO which could adjust thedanger level of cyanide exposure. As discussed above, CO and HCN are thetoxic twins of smoke inhalation. Even if the first and second comparisondeterminations indicate the absence of a dangerous level of cyanideexposure, the exposed individual may still be in danger due to COexposure. The comparison (932) and determination of an elevatedcarboxyhemoglobin level above a preset carboxyhemoglobin threshold(determination 934), when combined with an elevated thiocyanate levelabove the preset thiocyanate threshold (determination 914) alone orfurther with a depressed methemoglobin level below the presetmethemoglobin threshold (determination 924), leads to a conclusion of adangerous level of acute cyanide and carbon monoxide poisoning(conclusion 936). That is, a determination that the measured thiocyanatelevel is above the preset thiocyanate threshold (with or without adetermination that the measured methemoglobin level is below the presetmethemoglobin threshold) and the measured carboxyhemoglobin level isabove the preset carboxyhemoglobin threshold provides an indication ofacute cyanide and carbon monoxide poisoning for which medical treatmentis recommended to treat the health effects of the exposure for suchharmed individuals. The third comparison determination of CO exposurelevel (determination 934) is used to further reduce the likelihood ofdeath due to a combination of CO and cyanide poisoning.

FIG. 10 shows another example of a flow diagram 1000 illustratinganother method of detecting cyanide exposure. The method is also basedon measuring the presence or absence of elevated salivary thiocyanateand can be combined with measuring depressed methemoglobin values.

First, the thiocyanate level is measured (step 1010) to test for a highthiocyanate level above a first preset thiocyanate threshold, whichdistinguishes between salivary thiocyanate levels of concern and levelsnot of concern. The comparison (1012) and determination of an elevatedthiocyanate level above the first preset thiocyanate threshold(determination 1014) leads to a conclusion of a dangerous level of acutecyanide poisoning (conclusion 1016). The thiocyanate measurement step1010, comparison step 1012, and determination step 1014 may be similarto the thiocyanate measurement step 910, comparison step 912, anddetermination step 914, respectively.

Second, if the measured thiocyanate level does not reach above the firstpreset thiocyanate threshold in determination step 1014, themethemoglobin level is measured to test for a low methemoglobin levelbelow a preset methemoglobin threshold (step 1020). Next, the methodcompares the measured thiocyanate level with a second preset thiocyanatethreshold (which is lower than the first preset thiocyanate threshold)and compares the measured methemoglobin level with a presetmethemoglobin threshold (step 1022). If it is determined that themeasured thiocyanate level is higher than the second preset thiocyanatethreshold and the measured methemoglobin level is lower than the presetmethemoglobin threshold (determination 1024), it leads to the conclusionof a dangerous level of acute cyanide poisoning (conclusion 1026) forwhich medical treatment is recommended (or needed) to treat the healtheffects of the exposure.

Third, if (i) the measured thiocyanate level does not reach above thefirst preset thiocyanate threshold in determination step 1014, or (ii)it is determined in step 1024 that the measured thiocyanate level is nothigher than the second preset thiocyanate threshold and/or the measuredmethemoglobin level is not lower than the preset methemoglobinthreshold, the carboxyhemoglobin level is measured to test for exposureto CO (step 1030). Next, the method compares the measured thiocyanatelevel with a third preset thiocyanate threshold (which is lower than thefirst preset thiocyanate threshold and may be the same as or differentfrom the second preset thiocyanate threshold) and compares the measuredcarboxyhemoglobin level with a preset carboxyhemoglobin threshold(1032). If it is determined that the measured thiocyanate level is abovethe third preset thiocyanate threshold and the measuredcarboxyhemoglobin level is higher than the preset carboxyhemoglobinthreshold (determination 1034), it leads to a conclusion of a dangerouslevel of acute cyanide and carbon monoxide poisoning (conclusion 1036).If not, the process continues with the measuring and comparing or ends(1040).

Cyanide Exposure Detection Device

Thiocyanate is relatively non-toxic and concentrates in the saliva. Anaspect of the detection methodology is based on the rapid and reliabledetermination of thiocyanate in saliva using a photometric method. WhenFe(III) ions are added to samples containing thiocyanate, a red complexis formed, which is measured close to its absorption maximum at 492 nm.The photometric method permits the quantitative determination ofthiocyanate in small sample volumes and with a short sample preparationtime. In one example, a saliva sample from a potentially exposed personcan be placed in contact with a simple chemical indicator that willindicate, in conjunction with pulse oximetry measurements, whether ornot a high-level cyanide exposure has occurred. A low-cost samplecollection device with a colorimetric indicator such as iron nitrate canbe used to test for the presence of a high thiocyanate level in saliva.An example utilizes metal surfaces for detecting cyanide and relatedspecies, as disclosed in U.S. Pat. No. 7,776,610, which is incorporatedherein by reference in its entirety.

Another example involves the use of test strips which are covered on twosides by parafilm. The operator would peel open the parafilm to exposethe test strip. As used herein, the term “strip” is not limited to arectangular strip but may have any shape including a circular shapesimilar to that of a standard hole punch. Such a circle is the size ofthe test substrate suitable for the test, among other examples thatinclude rectangular and square test substrates. Saliva is a primecandidate as a test sample. The present disclosure is not limited tosaliva. Suitable test samples may include blood or other bodily fluids.

Color Calibration Curve

Establishing a calibration curve is an aspect of implementing thecyanide detection methodology using a cyanide exposure detection devicethat can be deployed to the front line to detect thiocyanate levels infront line workers such as firefighters and others such as fire smokevictims on-scene.

One way of establishing the calibration curve employs the Pena-Pereiraapproach. It may use the following materials: 1M nitric acid, 1Mthiocyanate solution, iron nitrate, artificial saliva (or distilledwater if artificial saliva is not available), Whatman #1 filter paper(Nitrocellulose based), roughly 35 mm² sample substrates from the filterpaper, either using a ¼-in hole punch or Pena-Pereira's method of usingink gel pens to block off areas (e.g., 6-mm squares), 2 μL pipette, anda camera.

An experiment may be carried out in accordance with Pena-Pereira exceptas noted. The user may prepare various thiocyanate concentrationsolutions and prepare 10 sample substrate filter papers per eachthiocyanate solution (for statistical analysis). The user may addthiocyanate solutions to the prepared filter substrates and record thecolor change with the camera after periods ranging from about 5 minutesto 2 weeks. The user can then use the image analysis algorithm toanalyze the captures images (i.e., Photometrix®). Based on the analysis,the user can establish a dose-color response calibration curve ofthiocyanate concentration.

FIG. 11 shows an example of salivary thiocyanate levels generated for adifferent context by Shashikanth Hegde et al., Estimation andcorrelation of salivary thiocyanate levels in periodontally healthysubjects, smokers, nonsmokers, and gutka-chewers with chronicperiodontitis, Indian J. Dent. Res. 2016; 27:12-4. The bar chart in FIG.11 shows the thiocyanate concentration for four groups (healthy,periodontitis, smokers, and gutka chewers) not related to smokeinhalation.

FIG. 12 shows the degree of color change with different concentrationsof thiocyanate according to one example taken from Pena Pereira et al.,Paper-Based Analytical Device for Instrumental-Free Detection ofThiocyanate in Saliva as a Biomarker of Tobacco Smoke Exposure 2016,Talanta, Jan 15 147. Measuring thiocyanate in saliva can be easily andcheaply determined by contacting saliva with iron nitrate on a teststrip. The test strip turns red. The degree of red depends onthiocyanate concentration. The darker the red, the higher the level ofthiocyanate indicating how much cyanide has been removed from the bloodstream.

A calibration can be achieved by testing and detecting a potential rangeof thiocyanate concentration after fire smoke exposure. If thethiocyanate level in saliva rises high enough and fast enough, and stayselevated long enough, and if sufficient distinction can be made betweenthe non-exposed general population's expected range of thiocyanateconcentration and levels shown by individuals exposed to cyanide smoke,and if further medical monitoring can determine what level shows nosignificant harm to the body, then an action level can be determined andthe test will be successful.

FIG. 13 shows notional different categories of concern based on thedegree of color change with different concentrations of thiocyanate.Some thiocyanate values will be of low concern because they are in arange normally exhibited by the population. Some concentrations will behigher than that but of moderate concern. It is expected that some ofthese levels of thiocyanate would not produce noticeable harmfuleffects. The highest levels would be of high concern because theyindicate a potential for severe health impacts. Field testing researchover time will allow levels of concern to be more definitivelydetermined.

Stability of Sampling Substrate

To test the stability of the sampling substrate, the user may employ thefollowing process. In the above experiment, the user may vary the timebetween substrate preparation and adding the thiocyanate from about 5minutes to 2 weeks. The user may store the prepared substrates inplastic zip bags (i.e., zip-top bags) at room temperature betweenpreparation and reuse. If the user observes a change, then the userrecords the degradation of color change with time (e.g., up to about 30minutes). This is not considered critical for the testing because it isanticipated that the testers will record the results immediately. If theuser does not observe a change, this step is skipped. Next, if theresults vary as expected in the first test, the user may try differentapproaches such as sealing the substrate or considering the use ofstabilizers. This will not need to be extensive because the user canperform the field tests by having the EMT (emergency medical technician)or the like add the indicator solution before use (although this is lessthan optimum).

Sample Collection

For the purpose of field testing, test subjects may be requested toexpectorate into a small weigh boat saliva sample and then 2 μL aliquotmay be drawn. Validating this will not occur in the lab until humansubject testing considerations are addressed or a laboratory withinnational laboratories that can perform such testing is found.

Production

Collected experimental data and conditions may be used to guide theproduction of robust and durable test kits which will be deployed forcyanide poisoning detection. A number of test substrates would bepackaged in accordance with the process for testing the stability of thesampling substrate as described above. The packaged test substrates canthen be individually used by trained testers (e.g., EMTs).

Field Testing

The field testing may involve collecting thiocyanate samples from aplurality of test individuals. Examples of test individuals includefirefighters before and after fire smoke exposure and thiocyanatesamples from fire smoke inhalation victims as well as unexposedindividuals. The goal is to identify a threshold level of thiocyanate orthreshold thiocyanate level that indicates a cyanide exposure at whichmedical attention is recommended. That level can be well above thenormal levels seen in the general population, making it less likely thatmedical attention would be sought that turned out not to be necessary.Additionally, there may be levels that will be above normal levels inthe population but below health hazard levels. The field testing willhelp identify this acceptable level that is below health hazard levelsfor which there is low to no concern. This may involve a subject whosebody is still relying on the reserve thiocyanate detoxification. Assuch, there may be three levels in the color change illustrated in FIG.13. The (first) normal low levels are really of low/no concern since thegeneral population all have such levels of thiocyanate anyway. The(second) moderate concern levels will be in that range where thethiocyanate is still detoxifying the body but is above normal levels. Itis not known whether those moderate levels are not producing someeffects. They may not merely be of low/no concern. The (third) highlevels are where damage can start and these would be actionable.

The field test may involve creating test strips that can be sent to thefield, collecting samples, and applying to the test strip forfirefighters before and after a fire and victims after being exposed.Initially multiple post-exposure tests over time can be performed tocharacterize the thiocyanate levels changing. The field test may furtherinvolve recording the concentration of thiocyanate, monitoring outcomesfor these firefighters and victims to relate thiocyanate levels withhealth effects, and based on the data, determining if an action level,indicating further monitoring or treatment is recommended, can bedefined. The field testing may conclude with identifying the thresholdlevel of thiocyanate that indicates a cyanide exposure at which medicalattention is recommended. The identified threshold thiocyanate level canbe set as the preset thiocyanate threshold. The testing device or testkit can be used for field use to test potentially dangerous levels ofcyanide exposure based on the predetermined threshold levels. Testresults may be quite immediate, and the potentially poisoned individualcan be promptly sent for further medical tests and treatment.

Field testing details may be determined with the testing organizationsuch as a municipal fire department. In one example, the firefighterswill have saliva tested before and after working an active fire. Toestablish thiocyanate timelines, samples may be taken and tested as soonas possible after the fire and then 3 further tests at 15-minuteintervals. The time for intervals may be adjusted as the data warrants.If possible, the victims would also be tested as soon as possible andthen at similar time intervals. The length of the time intervals is notcritical as long as it is recorded. The thiocyanate level of theindividual is measured after the individual is exposed to cyanide at atime of exposure, multiple times at different time intervals from thetime of exposure, and the measured thiocyanate level at each of themultiple times is compared to the preset thiocyanate threshold.

After each test, an image may be made to record the color change andrelevant data pertaining to the individual. The individual's name doesnot need to be disclosed. In addition to thiocyanate values, measurementof methemoglobin using a multi-channel pulse oximeter may be performedto monitor any changes as cyanide is detoxified and determine if acorrelation exists. If a firefighter or victim is judged to be cyanideintoxicated, if possible, medical center data such as methemoglobin orblood cyanide levels may be recorded. All data will be collected tofacilitate data analysis to determine thiocyanate action levels.

Front Line Detection of Cyanide Exposure

After determining the preset threshold values (including the presetthiocyanate threshold or first, second, and third preset thiocyanatethresholds for the first comparison determination of FIGS. 9 and 10,respectively, the preset methemoglobin threshold for the secondcomparison determination of FIGS. 9 and 10, and the presetcarboxyhemoglobin threshold of FIGS. 9 and 10), the cyanide exposuredetection device can be deployed to the front line to test thiocyanatelevels in front line workers such as firefighters and others such asfire smoke victims on-scene.

The thiocyanate level of the individual may be measured after theindividual is exposed to cyanide at a time of exposure, multiple timesat different time intervals from the time of exposure, and the measuredthiocyanate level at each of the multiple times is compared to thepreset thiocyanate threshold. This takes into account any changingvalues of the thiocyanate level over time after the exposure.

Similarly, the methemoglobin level of the individual may be measuredafter the individual is exposed to cyanide at the time of exposure,multiple times at different intervals from the time of exposure, and themeasured methemoglobin level at each of the multiple times is comparedto the preset methemoglobin threshold. This takes into account anychanging values of the methemoglobin level over time after the exposure.

The inventive concepts taught by way of the examples discussed above areamenable to modification, rearrangement, and embodiment in several ways.For example, different ways of measuring thiocyanate, methemoglobin, andcarboxyhemoglobin levels from those described herein can be used.

Accordingly, although the present disclosure has been described withreference to specific embodiments and examples, persons skilled in theart will recognize that changes may be made in form and detail withoutdeparting from the spirit and scope of the disclosure.

The claims define the invention and form part of the specification.Limitations from the written description are not to be read into theclaims.

An interpretation under 35 U.S.C. § 112(f) is desired only where thisdescription and/or the claims use specific terminology historicallyrecognized to invoke the benefit of interpretation, such as “means,” andthe structure corresponding to a recited function, to include theequivalents thereof, as permitted to the fullest extent of the law andthis written description, may include the disclosure, the accompanyingclaims, and the drawings, as they would be understood by one of skill inthe art.

To the extent the subject matter has been described in language specificto structural features and/or methodological steps, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the specific features or steps described. Rather,the specific features and steps are disclosed as example forms ofimplementing the claimed subject matter. To the extent headings areused, they are provided for the convenience of the reader and are not tobe taken as limiting or restricting the systems, techniques, approaches,methods, devices to those appearing in any section. Rather, theteachings and disclosures herein can be combined, rearranged, with otherportions of this disclosure and the knowledge of one of ordinary skillin the art. It is the intention of this disclosure to encompass andinclude such variation. The indication of any elements or steps as“optional” does not indicate that all other or any other elements orsteps are mandatory.

What is claimed is:
 1. A method of detecting cyanide exposure of anindividual, the method comprising: measuring a thiocyanate level of theindividual; comparing the measured thiocyanate level to a presetthiocyanate threshold to determine whether the measured thiocyanatelevel is above the preset thiocyanate threshold indicating a level ofacute cyanide poisoning for which medical treatment is recommended totreat health effects of the exposure; measuring thiocyanate levels of aplurality of test individuals after an exposure of the plurality of testindividuals to cyanide; measuring thiocyanate levels of at least some ofthe plurality of test individuals before the exposure of the pluralityof test individuals to cyanide; monitoring the plurality of testindividuals after the exposure for health effects of the exposure;identifying, out of the plurality of test individuals being monitored,one or more harmed individuals for whom medical treatment is recommendedto treat the health effects of the exposure; comparing the thiocyanatelevels of the at least some of the plurality of test individuals beforethe exposure, the thiocyanate levels of the one or more harmedindividuals, and the thiocyanate levels of the plurality of testindividuals after the exposure who are not the one or more harmedindividuals; determining, based on the comparing, a thresholdthiocyanate level above which medical treatment is recommended to treatthe health effects of the exposure; and setting the thresholdthiocyanate level as the preset thiocyanate threshold.
 2. The method ofclaim 1, wherein measuring the thiocyanate level comprises: placing abiological fluid of the individual in contact with a chemical indicatorto measure the thiocyanate level.
 3. The method of claim 2, wherein thebiological fluid comprises saliva.
 4. The method of claim 3, wherein thesaliva is collected using a swab or a strip.
 5. The method of claim 2,wherein the chemical indicator comprises a colorimetric indicator. 6.The method of claim 5, wherein the colorimetric indicator comprises ironnitrate.
 7. The method of claim 1, wherein the thiocyanate level of theindividual is measured after the individual is exposed to cyanide at atime of exposure, multiple times at different time intervals from thetime of exposure, and the measured thiocyanate level at each of themultiple times is compared to the preset thiocyanate threshold.
 8. Themethod of claim 1, wherein the thiocyanate levels of the plurality oftest individuals, after the exposure at a time of exposure, are measuredmultiple times at different time intervals from the time of exposure,and the measured thiocyanate levels including the thiocyanate levelsmeasured at the different time intervals after the time of exposure arecompared.
 9. The method of claim 1, wherein determining the presetthiocyanate threshold further includes: measuring thiocyanate levels ofa plurality of unexposed individuals who have not been exposed tocyanide; comparing the thiocyanate levels of the at least some of theplurality of test individuals before the exposure, the thiocyanatelevels of the one or more harmed individuals, the thiocyanate levels ofthe plurality of test individuals after the exposure who are not the oneor more harmed individuals, and the thiocyanate levels of the pluralityof unexposed individuals; determining, based on the comparing, thethreshold thiocyanate level above which medical treatment is recommendedto treat the health effects of the exposure; and setting the thresholdthiocyanate level as the preset thiocyanate threshold.
 10. A method ofdetecting cyanide exposure of an individual, the method comprising:measuring a thiocyanate level of the individual; comparing the measuredthiocyanate level to a preset thiocyanate threshold to determine whetherthe measured thiocyanate level is above the preset thiocyanate thresholdindicating a level of acute cyanide poisoning for which medicaltreatment is recommended to treat health effects of the exposure;measuring a methemoglobin level of the individual; and comparing themeasured methemoglobin level to a preset methemoglobin threshold todetermine whether the measured methemoglobin level is below the presetmethemoglobin threshold; a determination that the measured thiocyanatelevel is above the preset thiocyanate threshold and the measuredmethemoglobin level is below the preset methemoglobin thresholdproviding further indication of acute cyanide poisoning for whichmedical treatment is recommended to treat health effects of theexposure, as compared to the determination that the measured thiocyanatelevel is above the preset thiocyanate threshold.
 11. The method of claim10, wherein pulse oximetry is used to measure the methemoglobin level.12. A method of detecting cyanide exposure of an individual, the methodcomprising: measuring a thiocyanate level of the individual; comparingthe measured thiocyanate level to a preset thiocyanate threshold todetermine whether the measured thiocyanate level is above the presetthiocyanate threshold indicating a level of acute cyanide poisoning forwhich medical treatment is recommended to treat health effects of theexposure; measuring a carboxyhemoglobin level of the individual; andcomparing the measured carboxyhemoglobin level with a presetcarboxyhemoglobin threshold to determine whether the measuredcarboxyhemoglobin level is above the preset carboxyhemoglobin threshold;a determination that the measured thiocyanate level is above the presetthiocyanate threshold and the measured carboxyhemoglobin level is abovethe preset carboxyhemoglobin threshold providing an indication of acutecyanide and carbon monoxide poisoning for which medical treatment isrecommended to treat health effects of the exposure.
 13. A method ofdetecting cyanide exposure of an individual, the method comprising:measuring a thiocyanate level of the individual; comparing the measuredthiocyanate level to a first preset thiocyanate threshold to determinewhether the measured thiocyanate level is above the first presetthiocyanate threshold; if the measured thiocyanate level is above thefirst preset thiocyanate threshold, recommending medical treatment totreat health effects of the exposure; if the measured thiocyanate levelis not above the first preset thiocyanate threshold, then performing atleast one of (i) measuring a methemoglobin level of the individual,comparing the measured thiocyanate level to a second preset thiocyanatethreshold, which is lower than the first preset thiocyanate threshold,to determine whether the measured thiocyanate level is above the secondpreset thiocyanate threshold, comparing the measured methemoglobin levelto a preset methemoglobin threshold to determine whether the measuredmethemoglobin level is below the preset methemoglobin threshold, and ifthe measured thiocyanate level is above the first second presetthiocyanate threshold and the measured methemoglobin level is below thepreset methemoglobin threshold, recommending medical treatment to treathealth effects of the exposure; or (ii) measuring a carboxyhemoglobinlevel of the individual, comparing the measured thiocyanate level to athird preset thiocyanate threshold, which is lower than the first presetthiocyanate threshold, to determine whether the measured thiocyanatelevel is above the third preset thiocyanate threshold, comparing themeasured carboxyhemoglobin level with a preset carboxyhemoglobinthreshold to determine whether the measured carboxyhemoglobin level isabove the preset carboxyhemoglobin threshold, and if the measuredthiocyanate level is above the third preset thiocyanate threshold andthe measured carboxyhemoglobin level is above the presetcarboxyhemoglobin threshold, recommending medical treatment to treathealth effects of the exposure.
 14. The method of claim 13, wherein ifthe measured thiocyanate level is not above the first preset thiocyanatethreshold: measuring a methemoglobin level of the individual, comparingthe measured thiocyanate level to a second preset thiocyanate threshold,which is lower than the first preset thiocyanate threshold, to determinewhether the measured thiocyanate level is above the second presetthiocyanate threshold, comparing the measured methemoglobin level to apreset methemoglobin threshold to determine whether the measuredmethemoglobin level is below the preset methemoglobin threshold, and ifthe measured thiocyanate level is above the second preset thiocyanatethreshold and the measured methemoglobin level is below the presetmethemoglobin threshold, recommending medical treatment to treat healtheffects of the exposure; if the measured thiocyanate level is not abovethe first preset thiocyanate threshold or if the measured methemoglobinlevel is not below the preset methemoglobin threshold, measuring acarboxyhemoglobin level of the individual, comparing the measuredthiocyanate level to a third preset thiocyanate threshold, which islower than the first preset thiocyanate threshold, to determine whetherthe measured thiocyanate level is above the third preset thiocyanatethreshold, comparing the measured carboxyhemoglobin level with a presetcarboxyhemoglobin threshold to determine whether the measuredcarboxyhemoglobin level is above the preset carboxyhemoglobin threshold,and if the measured thiocyanate level is above the third presetthiocyanate threshold and the measured carboxyhemoglobin level is abovethe preset carboxyhemoglobin threshold, recommending medical treatmentto treat health effects of the exposure.
 15. The method of claim 13,wherein the thiocyanate level of the individual is measured after theindividual is exposed to cyanide at a time of exposure, multiple timesat different time intervals from the time of exposure, and the measuredthiocyanate level at each of the multiple times is compared to at leastthe first preset thiocyanate threshold among the first, second, andthird preset thiocyanate thresholds.
 16. The method of claim 13, whereinthe methemoglobin level of the individual is measured after theindividual is exposed to cyanide at a time of exposure, multiple timesat different intervals from the time of exposure, and the measuredmethemoglobin level at each of the multiple times is compared to thepreset methemoglobin threshold.
 17. A method of detecting cyanideexposure of an individual, the method comprising: determining a presetthiocyanate threshold; measuring a thiocyanate level of the individual;and comparing the measured thiocyanate level to the preset thiocyanatethreshold to determine whether the measured thiocyanate level is abovethe preset thiocyanate threshold indicating a level of acute cyanidepoisoning for which medical treatment is recommended to treat healtheffects of the exposure; determining the preset thiocyanate thresholdincluding: measuring thiocyanate levels of a plurality of unexposedindividuals who have not been exposed to cyanide; measuring thiocyanatelevels of a plurality of exposed individuals after an exposure of theplurality of exposed individuals to cyanide; monitoring the plurality ofexposed individuals after the exposure for health effects of theexposure; identifying, out of the plurality of exposed individuals beingmonitored, one or more harmed individuals for whom medical treatment isrecommended to treat the health effects of the exposure; comparingthiocyanate levels of the plurality of unexposed individuals,thiocyanate levels of the one or more harmed individuals, andthiocyanate levels of the plurality of exposed individuals after theexposure who are not the one or more harmed individuals; determining,based on the comparing, a threshold thiocyanate level above whichmedical treatment is recommended to treat the health effects of theexposure; and setting the threshold thiocyanate level as the presetthiocyanate threshold.
 18. The method of claim 17, wherein thethiocyanate levels of the plurality of exposed individuals, after theexposure at a time of exposure, are measured multiple times at differenttime intervals from the time of exposure, and the measured thiocyanatelevels including the thiocyanate levels measured at the different timeintervals after the time of exposure are compared.
 19. The method ofclaim 17, wherein the plurality of exposed individuals include at leastsome of the plurality of unexposed individuals before the exposure whobecome exposed individuals after the exposure.
 20. The method of claim17, wherein measuring the thiocyanate level comprises: placing abiological fluid of the individual in contact with a chemical indicatorto measure the thiocyanate level.